1. Field of the Invention
The present invention relates to a semiconductor light-emitting device using a nitride compound semiconductor, and to a manufacturing method thereof.
Priority is claimed on Japanese Patent Application No. 2006-327294, filed Dec. 4, 2006, the content of which is incorporated herein by reference.
2. Description of the Related Art
Recently, in various technical fields, techniques using light have been commonly used, and semiconductor light-emitting devices such as a GaN-type blue LED have been used as a device for emitting light.
Although such semiconductor light-emitting devices may use a light-transmitting substrate such as a substrate made of sapphire or silicon carbide, a silicon (Si) substrate may be used in consideration of cost reduction. However, silicon substrates do not transmit light. Therefore, light, which is emitted from an active layer and reaches a silicon substrate, does not pass through the silicon substrate, and is absorbed as heat or the like.
As a result, among the light emitted from the active layer, a light element, which is directed upward (i.e., to the side opposite to the silicon substrate), can be extracted, but a light element, which is directed downward (i.e., toward the silicon substrate), is absorbed as described above, and thus cannot be extracted.
Therefore, when using a silicon substrate, the output signal has a power of only ¼ to ⅕ of that obtained when using a light-transmitting substrate.
In consideration of such a problem, a structure has been disclosed, which has a substrate and a light-emitting part provided on one of main surfaces of the substrate, wherein a recessed part is provided in at least a part of the one of the main surfaces, an electrically conductive layer is provided in the recessed part, and light emitted from the light-emitting part is reflected by the conductive layer (see, for example, Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2006-237467). In accordance with the disclosed structure, as the light emitted from the light-emitting part is reflected by the conductive layer, it is possible to reduce a light element absorbed by the silicon substrate. Additionally, as the reflected light is directed upward, it is possible to improve light extraction efficiency on the upper side.
In accordance with the diagram showing the structure of the semiconductor light-emitting device in Patent Document 1, the distance between the center part of the active layer and the conductive layer provided in the recessed part in the horizontal direction seems not so large. However, the actual sectional structure of the semiconductor light-emitting device has a thin-sheet form. Therefore, in comparison with the route of light which is directly directed upward, the route from the center part of the active layer to the conductive layer (provided on a side of the active layer) is very large in plan view.
Therefore, in the above conventional semiconductor light-emitting device, light, emitted from the center part of the active layer to the side thereof; may be consumed as heat before it reaches the conductive layer (for reflecting the light upward) in the recessed part, that is, during the traveling toward the conductive layer.
Also in the above conventional semiconductor light-emitting device, when light is reflected in the recessed part, a part of the optical energy of the light is absorbed at a boundary between the conductive layer and the silicon substrate, and the absorbed energy is transformed into heat.
Additionally, with respect to the semiconductor light-emitting device disclosed in Patent Document 1, when filling a recessed part (provided in at least a part of one of main surfaces of the silicon substrate) with a conductive layer, the material for the conductive layer should have (i) a relatively excellent adhesion with respect to the silicon substrate, and (ii) a higher reflectance in comparison with the surface of the silicon substrate. In addition, an embedding process for filling the recessed part with the conductive layer is also necessary. Therefore, the total manufacturing cost is increased.